Thursday, October 28, 2021
No menu items!
Home Health How Long Does it Take for Benadryl to Work?

How Long Does it Take for Benadryl to Work?

You must have heard of Benadryl in mainstream media or from a friend, at least. It is an allergy medication that is accessible over the counter.

Medical research proves it is a safe and effective remedy as an antihistamine. So, how long does it take for Benadryl to work? And how long will it stay in your system? Read on as we explore this drug and provide you with the answers.

In recent years, socio-demographic surveys indicate that Benadryl is one of the leading causes of overdose deaths. However, far from these negative situations, this medicine is quite influential in the health and wellness sphere.

Benadryl At a Glance

  • Benadryl is the trade name for diphenhydramine.
  • Benadryl is often used for allergy-related reactions.
  • Injectable Benadryl takes about 5 – 10 minutes to realize any effects. When it is consumed orally, peak effects occur 15 – 20 minutes post-dosing.
  • Oral variants are more popular due to the accessibility and versatility of the product range.
  • Topical Benadryl can be used for insect bites.

What is Benadryl Used For?

Benadryl is the trade name for a chemical compound known as diphenhydramine. It is an antihistamine used to treat various illnesses and disorders such as insomnia and Parkinson’s Disease.

Anyone who has seasonal allergies may have already interacted with Benadryl. The medication is a popular choice of prescription used to bring relief for a range of disorders, including:

  • Allergic reactions
  • Sleep disorders
  • Skin conditions like rashes, itching, and hives
  • Motion sickness
  • Insect bites like bee stings
  • Coughs
  • Anxiety

Available Forms of Benadryl


The most popular type of Benadryl is oral variations. They are taken through the mouth. They include:

  • Tablets
  • Liquid-gels (liquid-filled capsules)
  • Chewable tablets
  • Oral liquid solution


Unlike the oral version, the Benadryl injection is only available through a prescription. It is a white, crystalline powder that’s dissolved in water and alcohol.

The injection is administered intravenously. And the recommended dosage for adults is 10 – 50mg. The maximum dose you’re allowed is 400mg. The dosing schedule is determined by your current condition and your response to treatment.


The Benadryl Itch Stopping Cream effectively treats hives, insect bites, or itchy skin due to allergies. Another topical product is Benadryl Itch Cooling Gel. The contents of these gels, creams, and sprays include diphenhydramine and other active ingredients like camphor and zinc.

A dermatologist is best placed to conduct a diagnosis and prescribe the best regimen for your skin condition. Therefore, if you are considering a Benadryl topical, schedule an appointment for a professional consultation.

The Science Behind the Curtain

Let’s get a bit technical. Every type of medication has a specialized way it interacts with your body’s organs and functions to realize specific effects. And it is the same when you take Benadryl.

Once ingested, it inhibits H1 (histamine-1) receptors to bring about relief from allergic reactions. The active ingredient, diphenhydramine, blocks histamine’s action on the body. As a result, it corrects symptoms like stomach cramps, itching, and airway narrowing (bronchoconstriction).

It also lowers serotonin re-absorption and disables cholinergic receptors and sodium channels, among other things. All this brings about an overall calming effect.

How Long Does it Take for Benadryl to Work

Benadryl reaches peak levels in the body within 2 hours. However, you may feel the effects of Benadryl much sooner. Benadryl is absorbed rapidly in the body. You’ll probably notice the effects within half an hour. An intravenous administration of Benadryl will work faster than taking it orally or applying a topical. The medicine should continue to work for about four to six hours.

Factors that Determine How Long it Takes for Benadryl to Work

So how long does it take for Benadryl to flush out of your system? Several factors influence how one would answer that question. They are:

  • Amount of drug one takes (dosage)
  • Frequency of use
  • General health and rate of metabolism
  • Interaction with other medication
  • Alcohol and other drugs

Read on as we explore each of these aspects in detail below.

Overall Health and Metabolism

The length of time it stays in the system is determined mainly by a person’s overall health. All medications are processed in the liver and excreted through the kidney. Thus, the health of both organs is crucial in this situation.

They should be able to drain the Benadryl out of your system if they are healthy and operating correctly. If either of them has a problem, the medicine will linger in the system for a more extended period.

In a similar vein, a person’s metabolism influences diphenhydramine flushing. When it comes to Benadryl, a faster metabolic rate means the medicine is expelled from your body more quickly.

The Dose

Suppose you were at a McDonald’s with a friend. You order a Big Mac, and she gets a McDouble. After 2 hours, she suggests you get a snack, which is okay. The problem is, you’re still feeling a bit stuffed from the last meal. That’s how dosage influences how long it takes for Benadryl to work.

The amount of diphenhydramine you take will have a significant impact on the amount of time Benadryl stays in your system. A person who takes a more significant dose of the drug may need more time to get the drug out of his system.

Let’s see a practical case – A patient ingests 100mg of Benadryl. After the half-life has expired, they will still have about 50mg of the drug in his system. A second patient is given 80mg. After the same amount of time had elapsed, they had 28mg residual Benadryl.

In the same way, it would take longer to feel hunger pangs after eating a Big Mac compared to a McDouble, a patient who took fewer doses would require less time to flush it out of the system.

Frequency of Use

The frequency with which diphenhydramine is administered has a significant impact on how long it stays in the body. The recommended dosage is once every 6 hours. When taken once a day, the effects quickly wear off, whereas when used a couple of times, the effects last longer.

However, consuming it only once a day may not be an effective technique for addressing the problem it is meant to address. If the medicine is taken every 6 hours, it may linger longer in the system, depending on the half-life of Benadryl.

Age of Patient

The half-life of diphenhydramine is determined in part by the individual’s age. It’s worth noting that the half-life of Benadryl is much shorter in adults and children than in the elderly. In the case of the former, they can get rid of Benadryl far more quickly than those over 65.

Medication Interactions

When diphenhydramine is taken with other medications, it has a noticeable effect on how long it stays in your system. When Benadryl is taken with some antidepressants, the amount of time it stays in your system is increased.

Brands like Monoamine Oxidase inhibitors cause an increase in side effects. Medication for coughs and hypertension and medicines like Zyrtec and Lorazepam may lengthen the time it takes for the effects to wear off.

Using diphenhydramine while you are on clonazepam (another anti-anxiety medication) magnifies the side effects. You may have trouble concentrating, become confused, experience dizziness and drowsiness. The effects are more intense. Motor coordination, judgment, and reasoning are impaired.

Drugs and Alcohol

It would be best if you never took Benadryl and alcohol together. Regardless of Benadryl’s half-life, mixing it with alcohol can have a surprising result. This could also affect how long Benadryl stays in your system.

The danger lies in the effects they evoke when mixed. Your CNS slows down too much, making it difficult to remain alert enough to handle mental and physical tasks.

I don’t think I even have to elaborate on how wrong it is to use harmful drugs when you’re on Benadryl. Drugs like heroin, fentanyl, and methamphetamine may inhibit the efficacy of Benadryl or enhance the severity of side effects.

For instance, taking Benadryl and cocaine predisposes you to organ failure. This is because the harmful drug influences extracellular dopamine levels, which cause physical and behavioral issues.

How Long Will it Take to Flush Benadryl from my Body?

In the Blood

Benadryl reaches its peak concentration in your blood within 4 hours of ingestion. Its blood level begins to drop at the end of the four hours.

It should take about four days for the final dose to stay in your blood after you ingest it.

In the Body

Benadryl’s half-life determines how long it lasts in your system. The diphenhydramine should be washed out of the system within two days.

However, you may be able to detect its presence in the urine for up to 4 days after consumption if you do a urine test.

In Your Saliva

Benadryl lingers in your saliva for the same amount of time it stays in your urine or blood. It would take about four days to get rid of all Benadryl in your system.

Can I Use Benadryl to Treat Anxiety?

You are probably wondering what business an antihistamine has to do with treating anxiety, as it turns out, quite a bit.

Anxiety is a normal part of life. We all experience anxiety at some point. It could be a pending interview, an upcoming event, or a looming exam. And it’s perfectly normal to be a little anxious sometimes. But if you have GAD (generalized anxiety disorder), you may have heard about Benadryl for anxiety.

Antihistamines are prescribed to treat allergic reactions. However, some short-term remedies brands may contain the active ingredient diphenhydramine. This raises the question, is it effective? And how does it work?

Antihistamines have a sedative effect on the brain. So taking a dose of Benadryl induces a state of relaxation from within, helping you feel less anxious. However, please consult with a doctor before you self-medicate.

An expert opinion is vital to determine if Benadryl is good for you. Plus, you get to answer how long does it take for Benadryl to work for anxiety.

Typically, the recommended dose for Benadryl for anxiety is 25 – 50ml. You will begin to experience the effects in about 15 – 30 minutes. You reach the peak after 2 hours.

Pros of Benadryl for Anxiety

You can purchase Benadryl without a prescription. It is sold over-the-counter in chemists and pharmacies. This makes it more accessible to people who need short-term treatment for anxiety.

Using this brand of antihistamine is also convenient and practical. It is fast-acting and delivers timely relief. Symptoms of mild anxiety fade away quickly.

Moreover, the risk of dependence and potential addiction is less with an OTC medicine for anxiety than prescription-based anti-anxiety medication.

The Downside

Drowsiness and sedation are common side-effects of taking Benadryl. The calming effect makes it easier to fall asleep. Due to this, it might be ill-advised operating heavy machinery or driving long distances.

Another prevalent con of using Benadryl for anxiety is availability. It is sold over-the-counter and can be misused if someone fails to observe caution.


The Internet is awash with diverse views regarding the use of Benadryl for different purposes. Don’t be fooled by online challenges encouraging ingesting more than the recommended dose. You risk overdosing on Benadryl.

Symptoms of Benadryl overdose include:

  • Seizures
  • Hallucinations
  • Heart arrhythmia

.A significant pitfall arises from the vastness of the digital market. It is almost impossible to regulate the Internet, and anyone can sell and buy anything online. This means there may be unscrupulous people posing as legitimate online pharmacies. And given the increase in the use of the Internet to purchase OTC drugs, all it takes is a few clicks and your order for Benadryl.

Therefore, take your time to research potential sellers before you transact with them. Your health is at stake, and you risk losing money to scammers on the internet.



Please enter your comment!
Please enter your name here

Most Popular

Recent Comments